Oscar North, a few weeks ago, when there was still a question as to whether there’d be a web interface to iCloud:

So if the truth does now reside in the Cloud then there must be a
way for you the user to tell iCloud about any lies your devices
might be telling it. And there is really only one way for Apple
to allow you to do this: It needs a canonical web interface that
allows you to roll back changes made to your iCloud by your
devices.

iCloud is based on the idea that there’s one canonical data store — the one “in the cloud”, stored in Apple’s data center. But it doesn’t necessarily follow that a web-based interface is necessary to manage it. This is what I was trying to express in my “It’s All Software” piece. A web interface is just another client.

Think about IMAP. The canonical storage is on the IMAP server. Your webmail is just another IMAP client accessing your email account — no more or less canonical than your desktop email client.